Electromagnetic relays have been used for a considerable number of years to enable the presence or absence of electrical energy to alternatively close and open a given electrical circuit. Typically, such relays comprise an electromagnetic motor which, when energized, attracts an armature from its retracted position to an attracted position to thereby move a pair of contacts either into or out of engagement. Usually, electromagnetic relays are employed between several electrical circuits such that when an electrical signal appears in a first circuit, the relay therein responds to complete or to open a second electrical circuit.
It has been realized for a considerable period of time that the electromagnetic strength applied to an armature varies considerably throughout its travel from its retracted position to its attracted position in engagement with a core or pole member which is part of the electromagnetic motor. That is, when the armature is retracted and thus is a maximum distance from the core, the magnetic permeability of the electromagnetic circuit is minimum due to the maximum air gap between the armature and core member. Thereafter, as the armature approaches the core member, the total permeability of the magnetic circuit increases due to diminution of the air gap, thus causing the electromagnetic force applied to the armature to increase accordingly.
For maximum efficiency in effecting movement of a moveable contact relative to a stationary contact, it is desirable to transmit a corresponding amount of force to the moveable contact, namely, a force which changes as the electromagnetic force on the armature changes. Ideally, in fact, it is desirable to have the force on the moveable contact increase at an even faster rate than the force developed between the armature and core member as the armature is attracted to its position of engagement with the core or pole member.